Microwave phase shifter



-April 22, 1969 F. J.- KASPER 3,440,570

MICROWAVE PHASE `SHIFTER Filed Oct. A1.2, 1967 United States Patent O 3,440,570 MICRWAVE PHASE SHHFTER Francis Ji. Kasper, Morristown, NJ., assignor to Bell Telephone Laboratories, Incorporated, Murray Hill, N .3., a corporation of New York Filed @et 12, 1967, Ser. No. 674,786 int. Cl. H01p 5/12, 5/14 U.S. Cl. 333-10 6 Claims ABSTRACT F THE DISCLOSURE Backgronnd of the invention This invention relates to electric phase Shifters and more particularly to phase shifters which may be electrically controlled at very rapid rates.

It is sometimes necessary to derive from an input signal two voltage vectors which are shifted in phase in opposite directions with reference to the input signal. An example of such a use is found in monopulse phased array radar applications which require a convenient means for rapidly varying the phase angles of two voltage Vectors. These are applied to the sum and difference channels of the radar to facilitate beam steering. Heretofore, phase Shifters having reactive components have been used in each array element for this purpose but, because they involve reactive components, they are frequency sensitive. The phase angle can be held more nearly constant over a wide frequency band if reactive elements can be avoided.

Summary of the invention The phase shifter of this invention comprises a circuit having two ports of a directional coupler coupled to two ports of a hybrid junction through two variable attenuators arranged to introduce attenuation in the coupled paths. These attenuators should be substantially free of reactance and they may either be independently adjustable or they may be ganged for simultaneous adjustment. An alternating signal introduced in a third port of the directional coupler results in output voltages at the remaining two hybrid junction ports, one output voltage advanced and the other retarded in phase through angles controlled by the attenuators. If the attenuators are ganged to simultaneously introduce attenuation in their respective paths and the voltage transmission coeflicient for one attenuator is made proportional to the sine and the coefficient of the other attenuator proportional to the cosine of an arbitrary angle, the phases of the two output voltages will be shifted through this same arbitrary angle and in opposite directions with reference to the input signal.

Brie]c description of the drawings The invention may be better understood by reference to the accompanying drawings in which:

FIG. 1 is a circuit diagram disclosing the essential features of an embodiment of the invention;

FIG. 2 is a vector diagram illustrating the phase relationships of the voltages at the several ports shown in FIG. 1; and

FIG. 3 is a fragmentary view of a conventional type of microwave attenuator suitable for the practice of this invention.

ICC

Detailed description The directional coupler 12 shown in FIG. 1 should have a coupling coefficient equal to one-half the square root of two, thereby identifying this coupler with those known in the art as a 3 db directional coupler. Directional couplers suitable :for the practice of this invention are disclosed in United States Patent 2,701,340 granted Feb. 1, 1955 to S. E. Miller and in an article by James K. Shimizu entitled Strip-line 3-db Directional Couplers published in the 1957 Institute of Radio Engineers Wescon Convention Record, vol. 1, part 1, pages 4-15.

Directional coupler 12 has four ports, 1, 2, 3 and 4 and hybrid junction 13 also has four ports, 5, 6, 7 and 8. Ports 3 and 4 of the directional coupler are coupled, respectively, to ports 5 and 6- of the hybrid junction through attenuators 10 and 11, attenuator 10 being included in the transmission path between ports 3 and 5 while attenuator 11 is included in the transmission path between ports 4 and `6. Port 2 of the directional coupler is connected to ground through an impedance 20 equal to the characteristic impedance of the coupler. It is assumed, of course, that all other ports also face impedances equal to the characteristic impedance. It is a property of directional couplers that a signal applied to the input port 1 will appear at port 3 ywithout suffering any substantial phase shift but will be reduced in amplitude by a factor equal to the coupling coeiiicient. A signal will also appear at port 4 equal in magnitude to that appearing at port 3 but shifted in phase by degrees. Under these conditions the voltage at port 2 `will be zero. Attenuator 10 will change the magnitude of the voltage received from terminal 3 by a factor determined by the amount of attenuation it provides and will deliver this voltage to port 5 of the hybrid junction. Similarly, attenuator 11 will change the amplitude of the voltage received from port 4 before delivering it to port `6 of the hybrid junction. In accordance with the preferred embodiment of the invention, attenuators 10 and 11 may be ganged through linkage 9 so that attenuation may be simultaneously changed in both transmission paths. Also in accordance with the preferred embodiment of the invention, the voltage transmission coeicient provided by attenuator 10 will be made to vary as the cosine of an arbitrary angle while attenuator 11 will be made to provide a voltage transmission coefficient in the lower transmission path proportional to the sine of the same angle. Alternatively, the gauging arrangement need not be used and the two attenuators may be independently adjusted at will to provide different phase shifts as desired. However, when the ganging arrangement is used, the voltages appearing at terminals 7 and 8 of the hybrid junction can be caused to shift in phase by equal amounts in opposite directions with reference to the voltage applied to input port 1 of the directional coupler.

To illustrate the circuit operation, it may be assumed that the input voltage V1 applied to port 1 is A sin wt as shown in FIG. 1. This voltage is shown as vector V1 in FIG. 2 at instant t with reference to axis 20. It is assumed that all of the vectors in FIG. 2 are rotating at the rate w counterclockwise about the origin 0 so that at instant t vector V1 will be at an angle equal to wt. This will be recognized as a standard convention for vector diagrams. The

than that of V1 by the factor 1/\/'2 and will -be in phase amplitude of voltage V3 appearing at port 3 will be less with voltage V1 as shown in the vector diagram. The voltage V4 appearing at port 4 will have the same magnitude as voltage V3 but will be retarded in phase with reference to voltage V3 by 90 electrical degrees. For these reasons, voltage V3 is represented as a sine function in FIG. 1 and voltage V4 is represented as a negative cosine function. The voltage V5 at port 5 will be in phase with voltage V3 but will be reduced in magnitude by the voltage transmission coeicient of attenuator 10 which is, as indicated in FIG. 1, equal to the cosine of the arbitrary angle a. Correspondingly, the voltage V6 at port 6 is in phase with the voltage V4 at port 4 but reduced in magnitude by the voltage transmission coefficient vof attenuator 11 which is, as indicated in FIG. 1, equal to sine a.

The voltages V5 and V6 at ports 5 and L6 combine vectorally in the hybrid junction 13 so as to produce a voltage V7 at terminal 7 and voltage V3 at terminal 8, each at one-half the magnitude of the input voltage V1. Voltage V7, however, is retarded in phase with reference to the input voltage V1 by the arbitrary angle introduced by the attenuators 10 and 11 while voltage V8 is advanced in phase by the same angle. These relationships are clearly shown in the vector diagram of FIG. 2. It will, therefore, be evident that as attenuators 10 and 11 are simultaneously adjusted to provide voltage transmission coefficients proportional, respectively, to the cosine and the sine of the arbitrary angle a, the phase relationships of voltage vectors V7 and V8 will increase and decrease with reference to the input voltage V1 as the arbitrary angle a is increased and decreased. This is a necessary requirement in deriving voltages for the sum and difference channels of monopulse radar systems for beam steering purposes.

Attenuators 10 and 11 in FIG. 1 have been shown symbolically, using standard symbols for such devices. If the steering is to remain within the first quadrant, most any microwave attenuator may be used but where the angles are to be varied through all four quadrants the microwave attenuator must be arranged to not only introduce the variable voltage transmission coeflicient but it must also be capable of reversing phase. While a perfectly useful device restricted for operation in one quadrant may be made, it is desirable in most modern radar applications that the attenuator be capable of operating in all four quadrants. An attenuator capable of this property is illustrated in FIG. 3 and is of the type disclosed in United States Patent 3,264,586 granted Aug. 2, 1966 to M. Rabinowitz.

FIG. 3 shows only one of the attenuators, for example, attenuator 10 of FIG. 1 which is connected between ports 3 and 5. This attenuator employs a 3 db directional coupler of the same type as coupler 12 in FIG. l. In comparing the directional coupler of FIG. 3 with coupler 12 in FIG. 1, it will be noted that ports 33 and 35 of FIG. 3 correspond with ports 1 and 2, respectively, of FIG. 1, while the ports corresponding to ports 3 and 4 of FIG. 1 are shown in FIG. 3 as ports 34 and 36 terminated by variable resistors 31 and 32 having equal resistances R. These resistors preferably comprise lPIN diodes which possess the property of changing their forward resistances as a function of a forward bias current. IPort 33 is coupled via blocking capacitor 37 to input terminal 3 and port 35 is coupled via blocking capacitor 40 to output terminal 5. Input terminal 3 and output terminal 5 of FIG. 3 are ports 3 and 5, respectively, of FIG. 1. The diodes 31 and 32 are connected between their respective coupler ports 34 and 36 and the ground plane of the coupler represented by the conventional ground symbol 50. r1`l1e coupler shown is of conventional strip-line construction; one conductive path comprises arm 44 starting from port 33 and terminating in port 36 via arm 47 while the other conductive path comprises arm 45 starting from port 35 and terminating in port 34 via arm 46. Coupling region 43 is common to both paths. The two paths are separated by a delectric layer 48 and it is to be understood that additional dielectric layers, not shown, separate the two conductive paths from a surrounding ground plane, also not shown but symbolically represented by ground v50. Bias current to the diodes is supplied in a conventional manner from current sources, not shown, connected to terminals 39 and 42 which are conductively connected to ports 33 and 35 via nductors 38 and 41, respectively.

As is well known, if the resistances R of resistors 31 and 32 are made equal to the characteristic impedance of the coupler, there will be no reections from their ports 34 and 36 so that energy entering at port 3 of FIG. 3 will not appear at port 5. As these resistances are caused to differ from the characteristic impedance, the voltage appearing at port S will increase in magnitude and will reverse in phase as the resistances R are varied through the characteristic impedance of the coupler. When the resistances R are made zero, the voltage at port 5 Will be out of phase with and about equal to the voltage at port 3 and as the resistances are caused to increase toward infinity, the voltage at port 5 will again approach the magnitude of the voltage at port 3 and will be in phase.

It will be evident to those skilled in this art that the invention is not limited to any particular kind of directional coupler providing it is arranged to have a coupling coeicient equal to l/V and that most any hybrid junction may be used providing it is capable of operating over the -microwave band and to have the properties described above.

What is claimed is:

1. A microwave phase shifter comprising a directional coupler and a hybrid junction, each having four ports, a rst transmission path coupling one of the directional coupler ports to one of the hybrid junction ports, a second transmission path coupling a second directional coupler port to a second hybrid junction port, an attenuator inserted in each transmission path so that an alternating voltage applied to a third port of said directional coupler will appear shifted in phase at the third and fourth hybrid junction ports by amounts controlled by the attenuators.

2. 'Ihe combination of claim 1 wherein the attenuators in the two transmission paths are ganged for simultaneous operation.

3. The combination of claim 1 wherein the attenuator in one of said transmission paths is so constructed and arranged as to provide a voltage transmission coeicient proportional to the cosine of an arbitrary angle While the attenuator in the other transmission path is so constructed and arranged as to provide a voltage transmission coefcient proportional to the sine of the same arbitrary angle, and means coupling said attenuators together for simultaneous operation.

4. A microwave phase shifter comprising a directional coupler and a hybrid junction, each having four ports, a rst transmission path coupling one of the directional coupler ports to one of the hybrid junction ports, a second transmission path coupling a second directional coupler port to a second hybrid junction port, means for connecting a third directional coupler port to a source of alternating voltage, and an attenuator means inserted in each of said transmission paths to simultaneously insert attenuation in said two paths so that the voltages appearing at the third and fourth hybrid junction ports will be simultaneously shifted in phase with reference to the voltage applied to said third directional coupler port.

5. The combination of claim 4 wherein said attenuator means provides a voltage transmission coefficient in said rst transmission path proportional to the cosine of an arbitrary angle and in said second transmission path proportional to the sine of the same arbitrary angle so that the phases of the voltages appearing at said third and fourth hybrid junction ports will be shifted in opposite directions by equal angular amounts.

6. A microwave phase shifter comprising a directional coupler and a hybrid junction, each having four ports, a first transmission path coupling one of the directional coupler ports to one of the hybrid junction ports, a second transmission path coupling a second directional coupler port to a second hybrid junction port, an attenuator means inserted in each of said transmission paths to provide a voltage transmission coeicient in one path 5 6 in accordance with the sine of an arbitrary angle and to References Cited simultaneously provide a voltage transmission coeicient UNITED STATES PATENTS in the other transmission path in accordance with the 3,323,080 5/1967 Schwelb et al. 33,3 11

cosine of the same arbitrary angle, whereby an alternating signal applied to a third port of said directional cou- 5 HERMAN KARL SAALBACH, Prima/W Examiner pler Will be advanced in phase by said arbitrary angle at MARVIN NUSSBAUM, ASSI-slant Exa,mne,.

a third port of said hybrid junction and retarded in phase by the same arbitrary angle at the fourth port of said U-S Cl- X-R- hybrid junction. 10 333-1 1f 29 

